1. Field of the Invention
This invention relates to polymeric coloring compositions. More particularly, it relates to soluble polymeric colorants, characterized as containing a substantial proportion of free amine groups.
2. Background Art
Polymeric colorants are composed of optically chromophoric groups bound to or into polymers. Such materials may be found in the prior art, for example, in Horiguchi et al.'s U.S. Pat. No. 3,337,288, granted on Aug. 22, 1967; in Wegman et al.'s U.S. Pat. No. 3,304,297, granted on Feb. 14, 1967; in Japanese Published Patent Application 14,434, published in 1966 and cited at 66 Chemical Abstracts 19843 j; in the article by Ida et al. appearing at pages 524-30 of volume 89(4) of YAKUGAKU ZASSHI; in Kalopissis's U.S. Pat. No. 3,567,678, granted on Mar. 2, 1971; in Dawson et al.'s U.S. Pat. No. 3,920,855, issued on Nov. 18, 1975; in the article by Dawson et al. appearing at pages 5996-6000 of volume 98:19 of JACS, and in Otteson et al.'s South African Patent Number 76/7083, filed Dec. 7, 1976. These and other references make it clear that in certain applications polymeric dyes can offer real, functional advantages. Their larger molecular size reduces their diffusivity and increases their film-forming properties. In food coloring applications polymeric colors can offer yet another advantage which is pointed out in the already-noted Ida et al., Dawson et al., and Otteson et al. references. If a polymeric color molecule has a large enough molecular weight and size, it will be too large to be absorbed from the gastrointestinal tract when eaten with food. This means that the color will not pass into the body, and any risk of systemic toxicity is essentially eliminated.
The polymeric colorant products disclosed in the cited Otteson and Dawson references and also, in fact, the products claimed in this application's parent may be classified as colorants that are water-soluble as a result of the presence of anionic groups such as sulfonates, sulfamates, phosphonates and the like, imparting hydrophilicity to the polymers. Such a method of solubilizing offers the major advantage of imparting water-solubility in a wide range of aqueous environments.
The present invention concerns soluble polymeric colorants which have amine solubilizing groups, but no significant number of anionic solubilizing groups. These materials offer particular advantages. They tend to be soluble in water at pHs of from about 2.0-4.0, but are insoluble in water otherwise. Their amine groups can ionically bond to negatively charged substrates. When applied to such a substrate, they are relatively colorfast not only because of their being bonded to the substrate, but also because of their limited solubility.